Data transfer between electronic computers may be achieved by means of light, such as laser light. A semiconductor laser device as shown in FIG. 1 may be frequently used as such laser light providing means, in which a plurality of light-emitting elements are disposed on a single substrate. If a laser device is of a type which emits a single light ray, a number of laser devices equal to the number of desired light rays must be provided, which requires a large space for such semiconductor laser devices and also increases the cost of the devices. Such problems can be solved by a semiconductor laser device such as the one shown in FIG. 1.
The semiconductor laser shown in FIG. 1 is shown and described in ELECTRONICS LETTERS, Vol. 24, No. 4, Feb. 18, 1988. Each one of light-emitting regions 1 is of a double-heterojunction structure and is disposed in one of light-emitting elements 8.
In operation, a forward bias is applied between a p-side electrode 4 and an n-side electrode 3 of a light-emitting element 8. Respective light-emitting elements 8 are electrically insulated from each other by separation grooves 10 disposed at boundaries 7 between adjacent elements 8. Thus, it is possible to cause respective elements to be individually excited to emit light.
Since only one light-emitting region is present for each light-emitting element 8 of the semiconductor laser device shown in FIG. 1, if even only one of a plurality of light-emitting regions 1 is found to be defective after the completion of the device, the entire semiconductor laser device must be rejected. regardless of whether the remaining light-emitting regions 1 are acceptable. Accordingly, the percentage of rejected semiconductor devices including a plurality of light-emitting elements 8 is higher than that of semiconductor lasers each including only one light-emitting element 8.
Furthermore, if any one of light-emitting elements 8 fails during operation, the semiconductor laser device including that light-emitting element must be replaced, which is not economical.
Another problem is that heat generated by each light-emitting region 1 is conducted to adjacent light-emitting elements 8 and thermally affects them. That is, heat generated by light-emitting elements 8 adversely affects the light-emitting characteristics of other elements 8.
Japanese Unexamined Patent Publication No. HEI 1-204235 discloses a semiconductor laser device including a plurality of light-emitting points on a single substrate with varying spacing between adjacent light-emitting points. If any one of the light-emitting points of a semiconductor laser device fails, another point cannot be a substitute for it, and, therefore, that laser device must be rejected.
Japanese Unexamined Patent Publication No. SHO 61-184738, Japanese Unexamined Patent Publication No. HEI 2-97082, and Japanese Unexamined Patent Publication No. SHO 63-111688 disclose semiconductor lasers including a plurality of light-emitting points which can be independently driven. However, the semiconductor laser devices also have the same problems as those associated with the above-described devices.
The present invention is to provide a semiconductor laser devices free of the above-described problems.